In the next generation mobile communication system such as the fourth generation system, a data rate exceeding 100 Mbps is required even upon high mobility. In order to satisfy this requirement, various wireless communication using a bandwidth of approximately 100 MHz has been studied. Of these, in particular, multicarrier transmission schemes represented by an OFDM (Orthogonal Frequency Division Multiplexing) scheme have been considered as important as transmission schemes for the next generation mobile communication system from the point of view of adaptability to a frequency selective fading environment and spectrum efficiency.
As one technique studied in order to realize high data throughput in the mobile communication system of the multicarrier transmission scheme, there is adaptive transmission control. In adaptive transmission control, a channel state is estimated for each subcarrier or each segment, and modulation parameters such as error correction performance, M-ary number, power, phase and transmission antenna are adaptively controlled for each subcarrier or each segment based on channel state information (CSI) indicating the result of this estimation. A segment is one part of the entire band used in multicarrier transmission and includes one or more subcarriers. The configuration and operation for controlling the modulation parameters for each segment are basically the same as the configuration and operation for controlling the modulation parameters for each subcarrier. To simplify the description, only modulation parameter control for each subcarrier will be described in the following description. Modulation parameter control for each segment is implemented by appropriately substituting “segment” for “subcarrier”.
There is a closed loop type in adaptive transmission control. Namely, an apparatus that receives information transmitted using subcarriers which are control targets feeds back CSI of these subcarriers. On the other hand, an apparatus that transmits information using subcarriers which are control targets, receives the feed back information, and adaptively controls the modulation parameters for the subcarriers based on this information.
In an example of adaptive transmission control of the related art, as shown in FIG. 1A, received power is individually measured for a plurality of subcarriers, and, as shown in FIG. 1B, a fixed number (in the same drawing, two) of neighboring subcarriers (in other words, subcarriers having the consecutive numbers assigned as identification information) are handled as a single subcarrier block. As shown in FIG. 1C, CSI obtained on a subcarrier block basis is then fed back to a transmitting side (for example, refer to non-patent document 1). The subcarrier block (or simply referred to as “block”) is one or more subcarriers gathered together, and more specifically, is defined as a group formed with one subcarrier or a neighboring plurality of subcarriers.
Further, in another example of adaptive transmission control of the related art, as shown in FIG. 2A, neighboring subcarriers where received power difference falls within a specific value (for example, ΔE) are handled as a single subcarrier block, and, as shown in FIG. 2B, CSI is calculated on the subcarrier block basis. Then, as shown in FIG. 2C, identification information for a head (or tail) subcarrier included in a given subcarrier block and CSI calculated for this subcarrier block are combined and fed back (for example, refer to patent document 1 and patent document 2).
Patent Document 1: Japanese Patent Application Laid-Open No. 2001-351971.
Patent Document 2: Japanese Patent Application Laid-open No. 2001-366285.
Non-patent document 1: “Multi-dimensional Adaptation and Multi-user Scheduling Techniques for Wireless OFDM Systems”, Brian Classon, Philippe Sartori, Vijay Nangia, Xiangyang Zhuang, Kevin Baum, IEEE International Conference on Communications 2003 (ICC2003), vol. 3, pp. 2251-2255, 11-15 May 2003